Sextus Empiricus preserves the argument of the lost book. Gorgias set out three theses, each in turn: first, that nothing exists; second, that even if anything exists, it cannot be apprehended by man; third, that even if it can be apprehended, it cannot be expressed or communicated to one's neighbour.
For that by which we communicate is speech, and speech is not the things themselves: we do not communicate the things that are, but speech, which is other than what exists. Just as the visible cannot become the audible, so what is cannot become our speech — and, not being speech, it cannot be made plain to another.
Whether the book was in earnest, a parody of Parmenides, or a rhetorician's demonstration that argument can establish anything, the ancients themselves could not decide.
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